1. Field of the Invention
This invention relates to a process for manufacturing a lead frame, more particularly to a process for manufacturing a multi-layer lead frame having at least one metal plate or plane, hereinafter referred to as "metal plane" which is used for a semiconductor device.
2. Related Art
A plastic package, whose speed and heat-radiation characteristics are as good as those of a ceramic package, has recently been developed. In addition, in place of a conventional single-layer lead frame, a multi-layer plastic lead frame for a semiconductor device has also been developed.
Such a multi-layer lead frame comprises at least one metal plane connected via an insulative layer to the bottom surfaces of inner leads. Using such a multi-layer lead frame, it will be possible to mount a relatively power-consumable semiconductor chip on the metal plane, due to a good heat radiation capacity of the metal plane. Also, the metal plane can be used as a ground layer or a power supply layer to improve the electrical characteristics of the semiconductor device.
FIG. 10 shows a conventionally known multi-layer lead frame which comprises three layers, i.e., a signal layer (i.e., lead frame 12) and two metal planes, i.e., a power supply metal plane 20 and a ground metal plane 62, which are laminated via insulative tapes 42a and 17b made of heat-resistant material including, such as a polyimide.
Using such a multi-layer lead frame, it would be possible to prevent a so-called cross talk which might be generated between signal lines and also possible to reduce the capacitance between the lines or inductance.
As shown in FIG. 10, in order to manufacture the above-mentioned multi-layer lead frame, at the first stage, a lead frame 12, a power supplying metal plane 20, a ground metal plane 62, and insulative tape pieces 42a and 42b each having respective surfaces providing with adhesive layers must individually be made. Then, these individual pieces must be positioned by using a special instrument, such as an image reader (not shown), and then heat-pressed to laminate and adhere them together.
However, in the above mentioned manufacturing process, it has been very troublesome and laborious work to position and laminate the five layers including the insulative tape pieces 42a and 42b by using the image reader. It also requires a lot of time and, therefore, an effective production rate would not be expected. In addition, when these pieces are released or disengaged from the gripping means after the pieces are gripped by the gripping means and laminated, the laminated pieces might be moved slightly and, therefore, a precise laminated multi-layer lead frame might not be obtained.
The multi-layer lead frame should originally have a good quality for multi-pin and, therefore, inner leads thereof are usually very dense. Thus, even a slight abberation might cause a disconnection between the terminals of the power supply plane 20 or the ground plane 32 and the corresponding inner leads of the lead frame 10.